2 - Anatomy of RF Waves

 

There are two important types of transmissions to understand: analog and digital. Analog signal transmission conveys information (such as sound, video, or data) through a continuous wave whose strength and frequency vary directly with a changing physical quantity at the source. Digital signal transmission involves converting information into ones and zeros, which are then formatted and sent as electrical pulses. The advantages of using digital signals include greater accuracy, noise reduction (minimizing unwanted signals), and an increased capacity for transmitting information.

The primary waveform we're going to discuss is what we call a sign or a sinusoidal waveform. The sinusoidal waveform is characterized by these curves.

Therefore, when examining this waveform, it's essential to understand its various components.

For example, at the top of the waveform, we have what's known as the crest. There is essentially a crest for every cycle of the waveform. On the opposite side of the waveform, we find the trough, which marks the bottom of the sinusoidal waveform. Running through the middle is the origin, also called the reference line.

The origin serves as our reset point. When examining the origin, we should expect to see that the distance from the origin to the crest is the same as the distance from the origin to the trough. This distance is known as the amplitude.

For instance, when we observe a similar sinusoidal wave pattern, although it doesn't extend as far, we are looking at a lower-amplitude version of the same waveform.

The period is a crucial factor here; it represents the amount of time it takes for one complete cycle to pass.

We can measure from any point on the waveform, if we measure to the exact same spot on the waveform at the end of the cycle. Naturally, we might consider the start of the cycle as when it crosses the origin and ends when it crosses the origin again in the same direction, going back up.

Lastly, we introduce the concept of phase. Phase is interesting because it requires comparing one waveform to another to understand it, as it is a relative concept. Currently, we can consider the phase to be at zero degrees.

We'll introduce another waveform that closely resembles the first one, except it lags slightly. This second waveform is said to be out of phase with the original. The distance between corresponding points on the two waveforms, such as the troughs, defines our phase difference.

Like the original waveform 'green', which we set as the zero-degree reference, we measure phase in degrees. For example, we might say our blue wave is 90 degrees out of phase with the original.

If we were to draw a waveform that is exactly opposite to the green waveform, always crossing the origin at the same point but going in the opposite direction, with troughs aligning with crests, it would be 180 degrees out of phase.

Frequency is a significant aspect of any Wi-Fi communication discussion. You're probably familiar with the concept of comparing a 2.4 gigahertz network to a 5 gigahertz network and to a 6 gigahertz network.

Whenever we discuss the concept of Hertz, we're engaging in a conversation about frequency. Frequency is essentially a measure of the number of cycles per second. Interestingly, the concept of cycles doesn't have a specific unit of measurement. Instead, we use 'one over second,' which is known as a Hertz.

Hertz is named after the scientist Heinrich Hertz, and it's important to capitalize the 'H' in 'Hertz' because it's a reference to a last name. For instance, if an entire wavelength occurs over one second and we count how many cycles there were, and we find 3 cycles in that second, the frequency of this waveform would be 3 Hertz—representing the number of cycles per second.

We can extend this to larger quantities. For example, if we have 1,000 cycles in a second, we will have 1,000 Hertz. We can abbreviate this as one kilohertz (1kHz), with 'kilo' representing a thousand. If we had 2,000 cycles, it would be 2 kilohertz (2kHz). When we talk about a million (1,000,000 cycles), we're referring to a megahertz (1MHz). Moving further, if we have a billion cycles (1,000,000,000), it's one gigahertz (1GHz), represented by 'giga,' which signifies one with nine zeros after it.

When we discuss Wi-Fi operating in the 2.4-gigahertz, 5-gigahertz, and 6-gigahertz ranges, we are referring to the frequency of the signal—how many cycles occur per second. gigahertz represents billions of these cycles happening within a single second.

To put this into perspective, let's compare Wi-Fi signals to visible light. We often use the acronym ROYGBIV to remember the colors of the visible light spectrum: Red, Orange, Yellow, Green, Blue, Indigo, and Violet.

The visible light spectrum spans from approximately 400 terahertz at the red end to around 800 terahertz at the high end where violet light resides. To understand terahertz, consider it in the context of computer data: just as a terabyte is 1,000 gigabytes, a terahertz is 1,000 gigahertz. When comparing, for instance, the 5-gigahertz Wi-Fi signal, which is on the higher end of our frequency spectrum, we are contrasting it with the low end of the visible light spectrum, which is approximately 400,000 gigahertz.

This illustrates the comparison of how much lower in frequency our Wi-Fi is compared to the visible light spectrum.

The wavelength of a waveform is somewhat like the period. In both cases, we select a point on the waveform, often near the center and close to the origin, and measure to that same spot at the end of the cycle. However, instead of measuring the time it takes, we measure the actual physical distance. Typically, we express wavelength in meters, although it can also be in kilometers or smaller units like millimeters, micrometers, nanometers, or picometers. The choice depends on the frequency of the waveform.

Wavelength and frequency are inversely proportional. When we increase the frequency, it means that within the same period, we will fit more cycles of the waveform.

We can observe that by squeezing our waveforms together, we effectively halved the wavelength. This change occurred because we increased the frequency, fitting more cycles within the same space. This relationship illustrates their inverse proportionality.

To find the wavelength when we have the frequency, we need to know the speed of the wave. This is why our earlier discussion about speed was crucial. In this context, the speed of the wave is the speed of light, denoted by the constant 'C' as mentioned previously.

λ = c/f (wavelength calculation formula

example: 3 = 10^8/3Hz

Answer: 1,000,000,000 meters is the wavelength of 3Hz

That's an extremely long wavelength, and it can be challenging to grasp just how large it is. If we set an RF wave to operate at 3 Hertz, the wavelength becomes enormous. However, as we increase the frequency of the wave, the wavelength starts to significantly shrink.

Happy Learning!!